Abstract: A generally closed loop fish rearing system and water conditioning apparatus, including a fish rearing tank with an aeration system and a generally flat floor, a biological means for removal of certain dissolved impurities, having an input conduit connected to the outlet in the fish rearing tank, a dissolved air flotation means for the removal of suspended solids and certain dissolved impurities, having an input conduit connected to the outlet in the biological means, and a fish rearing tank inlet conduit connected to the outlet in the dissolved air flotation means. The aeration system includes an air pressure means, and a distribution system. The distribution system includes a plurality of pre-fabricated air discharge holding means connected to the said conduits, and a plurality of aerating discharge means connected to said air discharge holding means to aerify and mix the water in said fish rearing tank.